Process for preparing colloidal ceric oxide and complexes thereof with free organic acids

ABSTRACT

A process is provided for preparing colloidal dispersions of ceric dioxide in inert organic media which comprises 
     (1) heating 
     (a) ceric dioxide comprising ammonium nitrate or ammonium and nitrate ions in an amount within the range from about 3 to about 14% by weight of the ceric dioxide and a member selected from the group consisting of water, methanol, acetic acid and mixtures thereof in an amount usually from about 10 to about 60 g per mole of CeO 2 , sufficient to effect reaction with 
     (b) an organic acid having from about ten to about forty carbon atoms 
     (c) an organic solvent selected from the group consisting of 
     (i) aliphatic and aromatic hydrocarbons, such as petroleum spirits, benzene, toluene, chlorobenzene, chlorotoluene, etc. 
     (ii) aliphatic and cycloaliphatic ethers, such as isopropyl ether or dicyclohexyl ether 
     (iii) aliphatic and cycloaliphatic ketones, such as diisobutylketone or cyclohexanone 
      at a temperature within the range from about 60° to about 200° C. thereby effecting dispersion of the ceric dioxide; 
     (2) removing water, methanol, acetic acid or mixtures thereof, and separating undissolved particles of solid material such as ammonium nitrate and undissolved cerium dioxide. 
     Association complexes are also provided, composed of ceric dioxide and organic acid having from about ten to about forty carbon atoms in a molar ratio CeO 2  /organic acid of at least 4:1.

This is a division of application Ser. No. 460,694, filed Jan. 24, 1983,now U.S. Pat. No. 4,545,923, which is a continuation-in-part of Ser. No.387,401, filed June 11, 1982, and now abandoned.

Metal soaps are well known for their application as driers used in paintand varnish formulations, to accelerate the drying of unsaturated oilssuch as linseed oil or unsaturated synthetic resins such as alkydresins. The metallic soap cation is assumed to actively catalyze theoxidation and polymerization processes, while the acid anion serves as acarrier for the metal, conferring oil-solubility, water-insolubility,and compatibility with the other components of the paint.

British Pat. No. 1,236,085 to Steel and Smith, published June 16, 1971,accordingly observes that it is obviously economically advantageous toincorporate as much metal per unit of acid as possible, providing theresulting soap is oil-soluble. This is achieved by the use of "basic"soaps, in which the ratio of metal to acid is greater than thestoichiometric ratio, for example:

    2RCOOH+PbO→(RCOO).sub.2 Pb+H.sub.2 O--Stoichiometric ratio

    2RCOOH+2PbO→RCOOPb.O.PbOOC.R+H.sub.2 O-- "basic" soap

However, the patent comments that in the preparation of "basic" soaps ofthis type the resulting solution of soap and oil is so highly viscous asto be very difficult to handle, particularly in the blending operationsnecessary in the manufacture of paint compositions. According to theBritish patent, this high viscosity can be reduced by reacting thereaction mixture of the carboxylic acid or alkali metal salt thereofwith a polyvalent metal salt or metal oxide providing the metal cationof the paint drier.

The polyvalent metal salt or metal oxide used in the process is a saltor oxide of aluminum, barium, copper, iron or magnesium, preferably ofzirconium, zinc or manganese, and most preferably of calcium, lead orcobalt. Mixtures of different metal soaps are recommended, inasmuch ascertain soaps such as the zinc and calcium soaps do not act as driers ontheir own, but exert a synergistic effect on other soaps, such as thecobalt or lead soaps. There is no reference to rare earth metal orcerium soaps.

British Pat. No. 972,804 to Turner, Downs and Harson, published Oct. 14,1964, describes metal organic soaps which contain aluminum or boron andat least one divalent metal element or metal radical, the aluminum orboron and the divalent metal atoms being linked through oxygen atoms,and at least one carboxylic acid radical. Such metal organic compoundsare obtained by condensing alkoxides or aryl oxides of aluminum or boronwith acyl oxides of divalent metals or metal radicals. The divalentmetals and metal radicals include magnesium, calcium, strontium, barium,zinc, cadmium, iron, cobalt, nickel, lead, copper, manganese and thezirconyl radical, but there is no reference to rare earth metals orradicals, such as cerium. The products have a high metal content, withorganic acid radicals present in the proportion of 0.5 to 1.5equivalents per metal atom. As a result, the products have a higher acidacceptance potential than conventional metallic soaps. These thereforeare an example of the kind of "basic" soaps referred to in British Pat.No. 1,236,085, discussed above.

British Pat. No. 1,430,347 to Collins and Pearl, published Mar. 31,1976, notes that the normal or "basic" metal soaps of syntheticcarboxylic acids have been compounds analogous to those previouslyderived from natural acids, or, in using different synthetic carboxylicacids as they become available, have presented compounds with a more orless homologous if not isomeric relation to each other. Collins et alpropose a departure from this prior art, using a different method ofpreparation, and a different composition, which results in a differentcharacter and properties of the resulting drier product or metal soap.

The prior art procedure according to Collins et al involves fusion orprecipitation methods. The reactant acid can be dissolved in anappropriate inert solvent, usually a hydrocarbon solvent such as mineralspirits, to which then is added the desired metal compound, usually inthe form of an appropriate oxide or inorganic compound or salt, withheating at an appropriate temperature to promote the reaction. Thisresults in a hydrocarbon solution of the soap, and the solvent can bedistilled off to increase the metal concentration to the desired value.

The Collins et al process utilizes a carboxylic acid or acid mixturewhich may be natural in origin, or derived from a natural product, or asynthetic product, and mixes this with a glycol ether or glycol or likepolyol, with addition also of a metal compound such as the metal powderor an oxide, hydroxide, acetate, or carbonate of the metal. This mixtureis then heated at a temperature from 65° to 143° C. until the metalcompound disappears, after which water is distilled off, the reactionmixture filtered, and excess glycol and glycol ether distilled off to anappropriate desired concentration or condition.

The equivalents ratio of metal to glycol ether or polyol is at least0.5, but a significant amount of the glycol ether or polyol must beretained in the product when it is desired to maintain fluidity. Theequivalents ratio for the metal moiety and the acid moiety is at least1.0, and when the metal is lead, at least 1.5, and ratios of 2 andhigher are easily obtained for lead. Barium, nickel and manganese soapsas well as cobalt soaps have been prepared by this method, in additionto lead. There is however no reference to rare earth metals, such ascerium.

The patentees note that their product and process are clearly distinctfrom the use of varying amounts of glycol or glycol ether merely toreduce the viscosity of the lead carboxylate, as in British Pat. No.1,148,998, or to stabilize soap solutions, as in Fisher U.S. Pat. No.2,007,553. These products are marketed by the assignee, MooneyChemicals, Inc.

Gamlen Europe SA, French Pat. No. 76 22426, publication No. 2,359,192,published Feb. 17, 1978, and British Pat. No. 1,571,210 published July9, 1980, provides organic cerium salts soluble in organic solventscharacterized by a ratio r of the number of acid equivalents to thenumber of cerium atoms of between 0.2 and 1, the number of acidequivalents meaning the number of acid molecules when the acid used inmonofunctional, and this number has to be doubled or trebled in the caseof diacids or triacids, and more generally multiplied by the number ofacid functions in the case of a polyacid. The cerium compounds thusprovided require a much smaller amount of acid than the amount usedpreviously with the same effectiveness, and also solutions of high metalconcentration reaching 500 g/l can be obtained which remain fluid andare capable of being handled without difficulty, while at the same timeremaining completely soluble in hydrocarbon media.

The organic acid can be any of RCOOH, RSO₃ H, ROSO₃ H, ROPO₃ H₂ or (RO)₂PO₂ H, where R is a hydrocarbon radical having at least seven carbonatoms. The organic acid radical can be a linear or branched aliphaticradical or a cycloaliphatic radical, which is optionally alkylated, oran aromatic radical, which is optionally alkylated. The cerium organicacid salts may contain at least one other rare earth metal element, inaddition, in an amount up to 25% of the total rare earth element contentincluding cerium. These compositions can be provided in the form oforganic solvent solutions of the cerium organic acid salt or mixturethereof containing more than 200 g/l of the composition. Thiscomposition can be included in paints or varnishes or liquid fuels.

The method for preparing these cerium organic acid salts or mixturesthereof comprises reacting (in organic or an aqueous organic medium) theorganic acid and freshly prepared cerium hydroxide Ce(OH)₃ under suchconditions that the resultant cerium organic acid salts have a ratio rof between 0.2 and 1. The reaction is preferably effected with heating,and preferably the organic medium is a hydrocarbon. After several hours,part of the water formed by the reaction separates spontaneously. Afterthe reaction, to assist in the separation of water from the reactionmedium, a further solvent can be added, such as a glycol, an alcohol oran alkyl glycol. The solution thus obtained can have its concentrationadjusted by addition of a suitable hydrocarbon.

In the working Examples, cerium hydroxide Ce(OH)₃ is obtained byprecipitating cerium nitrate with aqueous ammonia. The precipitate iswashed with water until nitrate ion has disappeared, and then filtereduntil it contains only 15% water. The cerium hydroxide is reacted with130 g of usual-grade oleic acid in white spirits at 80° C. Afterstirring for four hours, glycol is added, the separated water iseliminated, and then butyl-glycol is added, after which white spirit isadded to form the final solution.

It will be noted that it is with the cerous salts, not the ceric salts,that the patentees are concerned.

French patent application No. 81 09214, U.S. Pat. No. 2,482,075, andrelated cases therein discussed refer to the preparation of aqueousdispersions of cerium compounds that can be easily dispersed. By heatinghydrated ceria containing NO₃ ⁻, Cl⁻ or ClO₄ ⁻ for 1 to 2 hours attemperatures of from 200° to 450° C., a material is obtained that isdispersible in aqueous solutions. No indications are given, however,that the material can be dispersed in organic media.

Kirk-Othmer, Encyclopedia of Chemical Technology (Second Edition),Volume 4, p. 850, indicate that hydrated ceric oxide, also referred toas hydrous ceric oxide or cerium hydroxide CeO₂ xH₂ O, where x is anumber from 1/2 to 2, forms as a gelatinous precipitate when sodium orammonium hydroxides are added to solutions of ceric salts. It is usuallyreferred to as hydrous ceric oxide. When the precipitate is dried, ayellow hydrated oxide containing 85 to 90% CeO₂ results. Granular cerichydroxide may be made by boiling insoluble cerium salts withconcentrated sodium hydroxide, followed by washing and drying. Thecomposition and structure of these compounds depend on the method ofpreparation, and in many cases are uncertain. For this reason, it iscommon practice to express the composition in terms of equivalent CeO₂.

Cerous hydroxide Ce(OH)₃ forms as a white or off-white gelatinousprecipitate when solutions containing cerous ion Ce³⁺ are made alkaline.When allowed to stand for any length of time, a violet surface layer ofcerosoceric hydroxide appears.

Ceric oxide CeO₂ usually is made by igniting cerous oxalate or cerous orceric hydroxide in air. Ceric oxide is insoluble in acids, butdissolution is hastened by adding a small quantity of a reducing agent,such as an iodide or hydrogen peroxide. Eventually, strong nitric orsulfuric acid reacts upon heating.

In many applications, hydrated ceric oxide may be substituted for cericoxide. However, unlike cerous hydroxide, which is a classic type ofmetal hydroxide similar to Pb(OH)₂, Fe(OH)₃, etc., ceric hydroxide isactually hydrated ceric dioxide, also called hydrous ceric oxide, asnoted above. Accordingly, the term "ceric dioxide" as used in thisspecification and claims will be understood also to be inclusive ofceric hydroxide, hydrated ceric dioxide and hydrous ceric oxide, whichare all different names for essentially the same chemical, cericdioxide.

If pure ceric oxide is stirred and heated at a temperature in the rangeof from 60° to 200° C. in the presence of an aliphatic solvent, such aspetroleum spirits, or an aromatic solvent, such as toluene, and in thepresence of a carboxylic acid such as oleic, palmitic acid, ordodecylbenzene sulfonic acid, there is no dispersion. Neither is thereany other reaction with any other carboxylic acid, or alkyl or alkylarylsulphonic acid.

In accordance with the present invention, an entirely new type of highcerium content colloidal ceric dioxide is provided which can bedispersed in organic liquids, particularly organic solvents, as well ashigh cerium content compositions containing such colloidal ceric dioxidedispersed in an organic liquid. The high cerium content dispersions inaccordance with the invention are true dispersions as demonstrated bytransmission electron microscopy. The term "dispersed cerium dioxide" asused in this specification and claims indicates that the ceria particlesare of colloidal dimensions, and therefore exist in the form of acolloidal dispersion in organic liquids, but this does not exclude thepresence of ceria in solution, in addition to or instead of thecolloidally dispersed ceria. Transmission electron microscopy of thehydrated ceria before treatment in accordance with the invention doesnot show particles of colloidal dimensions. The conversion of this ceriato colloidal size particles is obtained during the treatment.

FIG. 1 is a transmission electron microphotograph showing thecrystalline particle form of a typical ceric dioxide prior to treatmentin accordance with the process of the invention; and

FIG. 2 is a transmission electron microphotograph showing the particleform of the ceric dioxide of FIG. 1 after treatment in accordance withthe process of the invention.

Colloidal ceric dioxide is obtained from ceric dioxide preparedespecially for use as a starting material in the process of theinvention in such a way as to contain in physical association therewith:

(1) from about 3 to about 14% of ammonium nitrate; and

(2) at least one of water, methanol, acetic acid and mixtures of any twoor three thereof in an amount within the range from about 10 to about 60g per mole of CeO₂.

Both (1) and (2) are essential, and must be present. This material isreferred to herein as "active ceric dioxide" or "active CeO₂ ".

It has been established by experimental evidence that the process of theinvention can be regarded as effecting a physical adsorption-additionreaction (as contrasted to a chemical substitution-elimination reaction,such as a salt formation) of the organic acid, possibly interstitially,or as an inclusion by chemisorption, into the ceric dioxide, whethercrystalline or noncrystalline. This association is formed upon thebreakdown of the large agglomerates of ceric dioxide into crystalliteswith diameters of about 50 Å while heating the active ceric dioxide asabove defined, and in the presence of a solubilizing organic acid of tento forty carbon atoms and an appropriate organic liquid at a temperaturewithin the range from about 60° to about 200° C., for a sufficient time,usually from 1 hour to about 24 hours, to effect the reduction of theagglomerates to colloidal size crystallites and their association withthe solubilizing acid, followed by removal of the water, methanol oracetic acid released, and filtering off the salts that separate uponcooling.

The CeO₂ -acid association complex can be isolated from such colloidalsolutions in solid colloidal particle form. Transmission electronmicroscopy of the colloidal solutions shows perfectly dispersedcrystallites of 50 Å. Provided it is kept in a closed container, thecomplex remains stable for some time. When mixed with an appropriateorganic liquid, a colloidal dispersion is obtained at once.

The starting ceric dioxide can be pure ceric dioxide, hydrous cericdioxide, or hydrated ceric dioxide, but it is essential that the ceriastarting material contain from about 3 to about 14% by weight ammoniumnitrate. The ammonium nitrate cannot be merely in admixture with oradded to the ceria, but must be in close physical association with theceria, possibly as an inclusion of ammonium nitrate as the salt moleculeand/or as ammonium and nitrate ions in the structure of the agglomeratesfound in the course of preparation of hydrated ceria. The secondrequirement is the presence in the system of the indicated amount ofwater, or methanol, or acetic acid, or mixture thereof.

The starting ceric dioxide suitable for making the products of theinvention is commercially available from Rhone-Poulenc. It can also beprepared in processes described in the patents, for instance, cerousnitrate or cerous carbonate treated with aqueous nitric acid followed byNH₄ OH--H₂ O₂ treatment, as indicated in French patent publication No.2,482,075. For the purpose of this invention, the ceric dioxide that isrecovered, for example, by filtration, centrifuging, or other separationtechnique, does not need to be washed, but if washed, it is not washedsufficiently to remove the occluded ammonium nitrate. It thus has inphysical association from about 3 to about 14% residual ammoniumnitrate, and also some cerium nitrate. The amount of nitrate may vary,depending on the process parameters selected in the manufacture, theamount of residual mother liquor, or the extent of partial washing, ifapplied. Understandably, when the base used for the precipitation is NH₄OH, the ions carried by the ceria will be those of NH₄ ⁺ and NO₃ ⁻.

The wet material as it comes from the filter contains also a variableamount of water. If the second requirement is to be met by waterpresent, it may be noted that at least about 10 g of water/mole of CeO₂is necessary for the wet material to be useful in the invention.Normally, the amount of water retained in the freshly prepared hydratedceria is from about 10 to 20%. Obviously, a higher water content can bepresent, but is a nuisance, since it has to be removed later on in theprocess.

Surprisingly, while methanol can be used in substitution for water,other lower alcohols such as ethanol are not effective, and cannot besubstituted for the methanol.

Similarly acetic acid is the only acid that can be substituted for thewater or the methanol; the organic acid used for preparation of theassociation complex cannot be used. The acetic acid as the water or themethanol has evidently a special function in the still not fullyunderstood mechanism of breaking the agglomerates to colloidal sizeCeO₂, followed by the addition of the solubilizing acid.

The amount of water or methanol or acetic acid or mixture thereof isfrom at least 10 up to about 60 g/mole CeO₂.

Prolonged drying of the ceria should not be carried out at such hightemperatures, as for instance at 375° C. or above, that ammonium nitratedecomposes, since then the NH₄ NO₃ content in the resulting ceria coulddrop below the required minimum amount, and the resulting ceria materialmay no longer be useful in the process of the invention, even with theaddition of water, methanol, or acid, and even free ammonium nitrate.

The organic liquid medium used in the process can be an inert aliphaticor cycloaliphatic hydrocarbon or mixture thereof, such as for example,mineral or petroleum spirits or mineral or petroleum ethers, which mayalso contain aromatic components. Examples include hexane, heptane,octane, nonane, decane, cyclohexane, cyclopentane, cycloheptane, andliquid naphthenes. Aromatic solvents, such as benzene, toluene, and thexylenes, are also suitable.

Chlorinated hydrocarbons such as chlorobenzene and chlorotoluene canalso be used, as well as aliphatic and cycloaliphatic ethers, such asdiisopropyl ether, and aliphatic and cycloaliphatic ketones. The organicliquid or solvent system will be selected taking into consideration thesolubilizing organic acid that is used, and the heating temperature, aswell as the ultimate application of the colloidal solution ordispersion. In some cases, a mixture of solvents is preferable. Theamount of liquid or solvent evidently determines the finalconcentration. Solutions containing up to about 50% CeO₂ are perfectlyfluid. It is therefore more economical and convenient to prepare morehighly concentrated solutions which later on can be diluted for use. Forthis reason the amount of solvent is not critical.

The organic acid forming the physical association complex is an organicacid or a mixture of acids that is soluble in the organic solvent mediumused. Aliphatic carboxylic acids, aliphatic sulphonic acids, aliphaticphosphonic acids, alkyl aryl sulphonic acids and alkyl aryl phosphonicacids having from about ten to about forty carbon atoms, natural orsynthetic, can be used. Exemplary are tall oil fatty acids, oleic acid,stearic acid, isostearic acid, lauric acid, 2-ethylhexoic acid,naphthenic acid, hexoic acid, toluene sulphonic acid, toluene phosphonicacid, lauryl sulphonic acid, lauryl phosphonic acid, palmityl sulphonicacid, and palmityl phosphonic acid.

The type of solubilizing organic acid used often determines the maximumamount of CeO₂ that can be dissolved. Alkyl aromatic sulfonic acids tendto afford preparation of products having higher concentrations of Ce.

The organic acid is used in an amount of at least 0.25 mole per mole ofCeO₂, inasmuch as the CeO₂ -acid physical association complex contains aratio of CeO₂ :organic acid of 4:1, as evidenced by the composition ofthe isolated solid form. While smaller amounts of acid can be used, anincomplete dispersion of the ceria may result, or a relatively unstabledispersion that will tend to deposit CeO₂. More than 0.25 mole oforganic acid can be used, but may not be necessary.

The presence of water, or methanol, or acetic acid, or mixture thereofis essential during the digestion time period, but their role is notwell understood. At least it can be said that they assist in theexpulsion of the nitrate ions in a manner resulting in the reduction ofthe CeO₂ agglomerations to colloidal size particles. The highly activesurface of the crystallites than adsorbs the acid that renders themorgano dispersible. If any of the essential activating volatilecomponents, such as water, methanol, or acetic acid is removed from thesystem before the desired processes have taken place, the reaction maynot take place at all, or can be incomplete.

Commercial grade hydrated ceria contain other rare earths as impurities.In some cases the presence of such impurities may be desirable for thebeneficial synergistic effects they may exhibit. Mixtures of ceriacontaining up to about 10% of other rare earths can also be used in thisprocess.

The overall heating can take from less than one hour up to about 24hours or longer, while heating and agitating at a temperature within therange from about 60° to about 200° C.

A preliminary heating of the starting ceric dioxide either as an aqueousslurry or in a mixture with the organic liquid such as petroleum spiritsat a temperature within the range from about 60° to about 200° C. forseveral hours followed by addition of the organic acid used in theformation of the physical association complex such as oleic acid resultsin significantly faster solubilization rates. Electron microscopicexamination of the heated material has revealed that no size reductionof the ceria particles has taken place, and thus it is believed thatduring the heating the crystallite bridges of ammonium nitrate and/orNH₄ ⁺ and NO₃ ⁻ ions are weakened, but not broken. It appears that underthe mild reaction conditions of the treatment, reduction of the ceria tocolloidal size is effected by adsorption of the organic acid such asoleic acid onto the ceria particles, which also renders the colloidalparticles dispersible in nonaqueous organic liquids or solvents. Thecolloidal dispersions produced by the described process thus is believedto contain the solubilizing acid as the free acid, and not in anyionized form. Thus, the cerium dioxide products described herein are notto be considered as cerium soaps, since these soaps are essentiallycerium salts of ionized fatty acids.

The following Examples in the opinion of the inventors representpreferred embodiments of the invention.

EXAMPLE 1

In a 3-necked reaction flask equipped with a stirrer, thermometer and acondenser were charged 55 g of active CeO₂ containing 77.5% of CeO₂(0.248 mole), 15.5% of water, and 7.0% of ammonium nitrate (asinclusions), 17.6 g of oleic acid (0.062 mole), and 35.0 g AMSCO solvent(aliphatic hydrocarbons). The mixture was stirred and slowly brought upto 90° C., and the temperature maintained for 2 hours with stirring. Thereaction started at 55° to 60° C., as indicated by the appearance ofwater droplets. During this time the solid suspension of CeO₂ changedinto a brownish colored colloidal solution containing visible water.Hexane was added, and the system azeotropically dried, whereby 8.5 g ofwater was collected. After removing most of the azeotroping agent, thedark brown colloidal solution was filtered. The CeO₂ content was 44%.

In contrast, pure cerium dioxide (99.5% CeO₂) was stirred in AMSCOsolvent in the presence of oleic acid at from 90° to 140° C. without andwith added water for 4 days, but no dispersion took place.

EXAMPLES 2 to 21

Following the same procedure as in Example 1, using the same active CeO₂and the same mole ratio of CeO₂ and acid, and solvent, but using theacid and solvent shown in Table I, the following ceria preparations weremade. In all cases, complete dispersion of the ceria was achieved.

                  TABLE I                                                         ______________________________________                                        Ex-                          Reaction Reaction                                ample                        Temperature                                                                            Time                                    No.   Solvent   Organic Acid (°C.)                                                                           (hours)                                 ______________________________________                                         2    Toluene   Stearic Acid  87      4                                        3    AMSCO     Isostearic   103-106   11/2                                    4    AMSCO     Lauric acid +                                                                              53-117   6                                                       Oleic acid                                                     5    Toluene   Dodecyl benzene                                                                             90      6                                                       Sulfonic acid                                                  6    AMSCO     Linoleic acid                                                                              60-101    0.45                                    7    Dichloro- Oleic acid    90      4                                             benzene                                                                  8    AMSCO     Myristic acid                                                                              62-118   6                                        9    Diisobutyl                                                                              Oleic acid   100      1                                             ketone                                                                  10    AMSCO     Coconut oil  100      4                                                       fatty acids                                                   11    AMSCO     Soya oil     100      3.5                                                     fatty acids                                                   12    p-chloro  Oleic acid   100      3                                             toluene                                                                 13    AMSCO     Naphthenic acid                                                                             90      6                                       14    AMSCO     Tallow fatty acids                                                                         85-93    1.5                                     15    Diisobutyl                                                                              Stearic acid 85-100   4.5                                           ketone                                                                  16    AMSCO     Linseed oil  70-104   1.5                                                     fatty acids                                                   17    AMSCO     Capric acid  88-115   4.5                                     18    AMSCO     Octoic* and  85-90    1.0                                                     oleic acids                                                   19    AMSCO     Pelargonic acid                                                                            85-109   3.5                                     20    Mesityl** Oleic acid   47-90    Over-                                         oxide                           night                                   21    Dibutyl   Oleic acid   65-95    Over-                                         ether                           night                                   ______________________________________                                         *2 ethylhexoic acid                                                           **with the addition of AMSCO to achieve clear solution                   

EXAMPLE 22

Active CeO₂ containing 80.17% CeO₂, 2.9% NH₄ NO₃, 16.9% H₂ O, vacuumdried at 95° C., containing 3.1 g of residual water per mole of CeO₂,was attempted to be dispersed following the procedure of Example 1,using the same solvent and oleic acid, but no reaction or dispersionresulted. Then, 12 g of methanol was added per mole of CeO₂, and themixture digested as in Example 1 for a period of 4 hours at 76° to 113°C. Complete dispersion resulted. The methanol and the water wereremoved, yielding a colloidal solution or dispersion in AMSCO containing45% of ceria.

EXAMPLES 23 to 25

Active CeO₂ of the composition indicated in Example 22 that wasoven-dried at 100° C. for 16 hours but still had a residual wateramounting to 6.6 g/mole of CeO₂ was heated with 0.25 mole of oleic acidper mole of CeO₂ with or without additional amount of water and underthe conditions outlined below in Table II.

                  TABLE II                                                        ______________________________________                                                        Total Amount                                                                              Reaction Reaction                                 Example         of Water    Temperature                                                                            Time                                     No.    Solvent  g/mole CeO.sub.2                                                                          (°C.)                                                                           (hours)                                  ______________________________________                                        23     Toluene  22          79-104   3.5                                      24     AMSCO    19.6        67-109   Overnight                                                                     (15 hours)                               25     AMSCO    6.6         50-140   48                                       ______________________________________                                    

Dispersion in Examples 23 and 24 was complete, but incomplete in Example25. Example 25 thus indicates that 6.6 g water per mole of CeO₂ is onthe borderline, as the dispersion was not complete.

EXAMPLES 26 to 28

Active CeO₂ containing 75% CeO₂, 6.5% NH₄ NO₃, 16.9% H₂ O, wasoven-dried at 175° C. for 72 hours. Oleic acid 0.25 mole/mole of CeO₂was used as the organic acid under the conditions shown under Example26.

Next, the dehydrated ceria was digested with added water (Example 27) orethanol (Example 28) in the amount indicated in Table III for the timeand at the temperature indicated in Table III.

                  TABLE III                                                       ______________________________________                                        Example                    g/mole Temp.  Time                                 No.     Solvent  Added     of CeO.sub.2                                                                         (°C.)                                                                         (hours)                              ______________________________________                                        26      Toluene  None      --     90-110 48                                   27      AMSCO    Water     33     55-90   4                                   28      Toluene  Ethanol   24     90-110 48                                   ______________________________________                                    

Only Example 27 went as desired to complete colloidal solution ordispersion. Example 26 did not contain water, and Example 28 had ethanolbut not water or methanol, and neither gave any apparent dispersion ofthe ceria.

EXAMPLES 29 to 30

Active CeO₂ of the preceding Examples 26 to 28 was azeotropically driedwith toluene. Methanol (Example 29) or acetic acid (Example 30) was thenadded with oleic acid, and the dry powder was then dispersed under theconditions shown in Table IV.

                  TABLE IV                                                        ______________________________________                                        Ex-                                Reaction                                   am-                                Temper-                                    ple                         g/mole ature  Reaction                            No.  Solvent  Acid    Added of CeO.sub.2                                                                         (°C.)                                                                         Time                                ______________________________________                                        29   Toluene  Oleic   MeOH  10.0   74-88  Over-                                                                         night                               30   Toluene  Oleic   Acetic                                                                              18.0   67-102 Over-                                                     Acid                night                               ______________________________________                                    

EXAMPLE 31

The active CeO₂ of Example 1 was heated at 350° C. for 24 hours. Theceria was then mixed with AMSCO, oleic acid and water, and digested asin Example 27. No dispersion was observed after several days heating,even after adding methanol or aceitc acid to the reaction mixture.

EXAMPLE 32

A 20 g sample of the colloidal solution prepared in Example 1 was slowlypoured into 100 g acetone at room temperature. After stirring for a fewhours at room temperature, the solid was filtered out and washed severaltimes with acetone. The vacuum dried solid showed by analysis thefollowing composition:

57.9% Ce

21.11% C

3.48% H₂

16.51% O₂ by difference

Empirical formula: Ce₄ C₁₈ H₃₈ O₁₀

Chemical Formula: (CeO₂)₄ (oleic acid)

The solid obtained as described is soluble in inert aliphatic orcycloaliphatic hydrocarbons, ketones and ethers, and chlorinatedaromatic hydrocarbon solvents. The transmission electron microphotographof this material is shown in FIG. 2. Although the acid is stronglyadsorbed onto the surface of the ceria, a simple extraction withmethanol yielded free acid in an amount of about 10% of the acidtheoretically adsorbed.

This suggests that the oleic acid is adsorbed onto the surface of theceria particles produced during the dispersion process. Support for thisproposal was obtained from consideration of the infrared spectraobtained for the starting the final products. The carbonyl stretchingvibration of free oleic acid was determined to be 1708 cm⁻¹, and thisvalue is exactly in the range anticipated for a carboxyl group attachedto an aliphatic chain. In the IR spectra of the mulled solid or originaldispersion, no evidence for free oleic acid can be found. However, astrong (but broad) band is noted at 1510 cm⁻¹ (not due to solvent), andwe assign this feature as being due to the perturbed carbonyl stretchingmode of adsorbed oleic acid.

EXAMPLE 33

Commercial grade hydrated ceria containing 8.36% of ammonium nitrate and21.34% total of water was stirred with oleic acid in AMSCO as in Example1 at 90° C. Dispersion was achieved in 17 hours.

A sample of the same grade hydrated ceria (62.15 g) was mixed with 14.4g of water and heated at 90° to 100° C. for 5 hours. The excess of waterwas removed by filtration, 17.59 g of oleic acid and 34.95 g of AMSCOwere added, and the mixture was heated at 90° C. The dispersion wasaccomplished in 4 hours instead of 17.

One hundred gram sample of the hydrated ceria used in Example 33 washeated at 400° C. for 16 hours, resulting in 71.8 g dry powdercontaining 70.3 g cerium dioxide and 1.5 g of nitrates.

Mixing 43.9 g of the dried material with AMSCO and oleic acid with orwithout water gave no dispersion after 24 hours of heating at 90° C.

EXAMPLE 34

A sample of the active CeO₂ used in Example 4 was heated in AMSCO onlyfor 6 hours at 90° C., and then the oleic acid added. The dispersion wastotal in 1.5 hours after the addition of the acid.

Having regard to the foregoing disclosure, the following is claimed asthe inventive and patentable embodiments thereof:
 1. An associationcomplex comprising ceric dioxide and an organic acid having from aboutten to about forty carbon atoms in a molar ratio CeO₂ /organic acid ofat least about 4:1, in the form of a CeO₂ -acid association complex insolid colloidal particle form, forming a colloidal dispersion when mixedwith an organic liquid.
 2. An association complex according to claim 1in which the organic acid is oleic acid.
 3. An association complexaccording to claim 1 in which the organic acid is lauric acid.
 4. Anassociation complex according to claim 1 in which the organic acid isisostearic acid.
 5. An association complex according to claim 1 in whichthe organic acid is tallow fatty acids.
 6. An association complexaccording to claim 1 in which the organic acid is linseed oil fattyacids.
 7. An association complex according to claim 1 in which theorganic acid is benzene sulfonic acid.
 8. A colloidal dispersion is anorganic liquid comprising an association complex according to claim 2dispersed in an organic solvent.
 9. A colloidal dispersion in an organicliquid comprising an association complex according to claim 3 dispersedin an organic solvent.
 10. A colloidal dispersion in an organic liquidcomprising an association complex according to claim 4 dispersed in anorganic solvent.
 11. A colloidal dispersion in an organic liquidcomprising an association complex according to claim 5 dispersed in anorganic solvent.
 12. A colloidal dispersion in an organic liquidcomprising an association complex according to claim 6 dispersed in anorganic solvent.
 13. A colloidal dispersion in an organic liquidcomprising an association complex according to claim 7 dispersed in anorganic solvent.